1. Field of the Invention
This invention relates to an apparatus for detecting an obstacle to a power regulated window for detecting existence of an obstacle in a window glass driven by a power regulator in a vehicle.
2. Description of the Related Art
Generally in a vehicle especially a passenger car, a power regulated window for opening/closing a window glass such as a door window automatically by motor drive controlled by switch operation is applied. These days, an apparatus for detecting an obstacle for detecting whether or not an obstacle such as an article or a part of a human body is bitten between a window glass and a door frame is additionally provided on the power regulated window.
FIG. 6 shows an apparatus for detecting an obstacle to a power regulated window as one general example. A method of current differential to judge existence of an obstacle when a current differential value exceeds a predetermined constant value by detecting change (differential value) of current flowing through a motor for driving a power regulated window is applied to the apparatus.
The apparatus includes a current sensor Si connected in series with an armature of a motor M between a plus power source +V and a ground for detecting current flowing through the armature and outputting a value converted from the current to voltage, an amplifier AMP for outputting a momentary value of voltage Vins (call momentary value hereafter) by amplifying the converted-to-voltage armature current into predetermined voltage range, an averaging circuit AV for outputting an average value Vav by averaging the momentary value Vins with a fixed time constant, a threshold setting portion (not shown) for reducing the amplified momentary value Vins entirely under the average value Vav to set a threshold value for judgment between the momentary value Vins and the average value Vav, and a comparator CMP for comparing the momentary value Vins after being reduced to the voltage range with the average value Vav. The averaging circuit AV is provided with a capacitor C for setting the time constant.
Operation of the apparatus will be described.
In the current sensor Si, the current flowing through the armature of the motor M for driving the power regulated window flows a not-shown resistor to detect the current value converted to a voltage value and the voltage value as a momentary value Vins is transmitted to the amplifier AMP to be amplified to the predetermined voltage range.
The amplified momentary value Vins is transmitted to the averaging circuit AV having a fixed time constant to be averaged as the average value Vav inputted into the comparator CMP. After the amplified momentary value Vins is reduced entirely constantly under the average value Vav in the threshold setting portion in which the threshold value is set in a minus voltage, the momentary value Vins is inputted into the comparator CMP.
The momentary value Vins follows under the threshold value for judgment Vsh from the average value Vav to have slower change of current (di/dt1) of the momentary value than change of current by the time constant of the averaging circuit AV, unless the motor is overloaded, as shown in FIG. 7. Therefore, the momentary value Vins is maintained constantly under the threshold value for judgment Vsh from the average value Vav so that the comparator CMP never output a signal of judgment of existence of an obstacle OUT1.
When an obstacle such as a finger is clamped by the window glass during closing the window and overcurrent flows through the motor M, the momentary value Vins has faster change (di/dt2) than change by the time constant of the averaging circuit AV so that the momentary value Vins over the slowly changing average value Vav is inputted into the comparator CMP. Thereby, the comparator CMP outputs a signal of judgment of existence of an obstacle OUT1.
3. Objects to be Solved
The apparatus, as mentioned above, judges existence of an obstacle when the ratio of change di/dt of the momentary value exceeds the fixed value. However, if an obstacle to a window exists when the drive voltage is reduced by low temperature around the motor and steady rotating speed is very slow, the obstacle could not be detected by change of the momentary value Vins.
The average value Vav as a reference value for judgement of existence of an obstacle is generated to smooth the momentary value with a predetermined time constant so that the average value follows to the momentary value correspondingly to slower change of current (the momentary value) than the time constant.
To solve the above drawback, it can be considered for detecting an obstacle in low rotating speed to enlarge the time constant of the averaging circuit for generating more slower change of the average value than the slow change of the momentary value. In this apparatus, if, at high drive voltage and high rotating speed of the motor, the momentary value changes excessively by overloading on the motor caused by the other than existence of an obstacle such as resistance force against sliding window enlarged by temperature change of outside, the momentary value may exceed the average value easily and existence of an obstacle may be detected unexpectedly. Therefore, the time constant can not be enlarged over a certain value.
To solve the above drawback, a method of detecting an obstacle by providing a circuit for calculating a deferential value with the absolute value of a difference between respective values of momentary current at each time interval in low rotating speed, and detecting an obstacle with the absolute value of a difference between respective values of momentary current when an obstacle can not be detected with the deferential value of the momentary current may be applied. However, the reference absolute value can not be set low enough in this method so that, when an obstacle exists, an obstacle can not be detected until the momentary current over a predetermined reference absolute value flows, and then a force of biting an obstacle is increased.
To overcome the above drawback, one object of this invention is to provide an apparatus for detecting an obstacle to a power regulated window, which can detect the obstacle by a method of differential current at low rotating speed of a motor and reduce a force of biting the obstacle and also prevent from detecting existence of an obstacle unexpectedly at high rotating speed of a motor.